Arc discharge lamps of the high pressure sodium variety comprise an arc tube, usually of alumina, which is hermetically sealed and has an electrode in each end. Within the arc tube are quantities of mercury and sodium and a fill gas which is selected from the rare gases but is usually xenon at a pressure of 14-30 torr.
HPS lamps typically are started with a high voltage pulse in the range of 2 KV-3 KV, with a one microsecond width. This pulse is derived from the ballast, and, in the United States, the range and magnitude of this pulse are specified by ANSI.
It is known that the luminous efficacy (usually denoted as lumens per watt) of HPS lamps can be increased by increasing the xenon pressure (see U.S. Pat. No. 3,248,590).
However, it is also known that increasing the xenon pressure raises the breakdown voltage of the lamp to the point that the standard ANSI pulse fails to start the lamp.
One means to overcome this deficiency is the use of a starting aid, and several forms of such aids have been suggested--see, for example, Journal of the Illuminating Engineering Society, January 1978, pg. 125.
Other forms of starting aids are shown in U.S. Pat. Nos. 4,179,640; 4,137,483; and 4,146,813. While the starting aids described above work well enough on new lamps, problems with starting appear as the lamps age.